Human RSV or Respiratory Syncytial Virus is a large RNA virus, member of the family of Paramyxoviridae, subfamily pneumoviridae together with bovine RSV virus. Human RSV is responsible for a spectrum of respiratory tract diseases in people of all ages throughout the world. It is the major cause of lower respiratory tract illness during infancy and childhood. Over half of all infants encounter RSV in their first year of life, and almost all within their first two years. The infection in young children can cause lung damage that persists for years and may contribute to chronic lung disease in later life (chronic wheezing, asthma). Older children and adults often suffer from a (bad) common cold upon RSV infection. In old age, susceptibility again increases, and RSV has been implicated in a number of outbreaks of pneumonia in the aged resulting in significant mortality.
Infection with a virus from a given subgroup does not protect against a subsequent infection with an RSV isolate from the same subgroup in the following winter season. Re-infection with RSV is thus common, despite the existence of only two subtypes, A and B.
Today only three drugs have been approved for use against RSV infection. A first one is ribavirin, a nucleoside analogue that provides an aerosol treatment for serious RSV infection in hospitalized children. The aerosol route of administration, the toxicity (risk of teratogenicity), the cost and the highly variable efficacy limit its use. The other two drugs, RespiGam® (RSV-IG) and Synagis® (palivizumab), polyclonal and monoclonal antibody immunostimulants, are intended to be used in a preventive way. Both are very expensive, and require parenteral administration.
Other attempts to develop a safe and effective RSV vaccine have all met with failure thus far. Inactivated vaccines failed to protect against disease, and in fact in some cases enhanced disease during subsequent infection. Life attenuated vaccines have been tried with limited success. Clearly there is a need for an efficacious non-toxic and easy to administer drug against RSV replication. It would be particularly preferred to provide drugs against RSV replication that could be administered perorally.
WO-2006/026135 discloses substituted biaryl piperazinyl-pyridine analogues for use in the treatment of conditions related to capsaicin receptor activation. WO-2008/008453 discloses heterocyclic substituted piperazine compounds with CXCR3 antagonistic activity. WO-2008/099210 discloses heteroarylpiperazine derivatives for treatment of Alzheimer's disease and related conditions. WO-2011/143129 discloses nitrogen-heterocyclic compounds as phosphodiesterase 10 inhibitors.
EP-2,149,373 discloses substituted piperazinyl compounds as 5HT7 receptor ligands. Foks H. et al. in Phosphorus, Sulfur, and Silicon, vol. 180, pp. 2543-2548 (2005) disclose a number of substituted piperazinyl compounds having tuberculostatic activity. WO-2011/015037 discloses compounds having antiviral activity by inhibition of the nucleoprotein of the virus, in particular influenza virus, whereby in one embodiment these compounds are heterocyclic amides containing piperazine and isozazole rings substituted with one or more substituents.
It is desired to provide new drugs that have antiviral activity. Particularly, it would be desired to provide new drugs that have RSV replication inhibitory activity. Further, it would be desired to retrieve compound structures that allow obtaining antiviral biological activities of the order of magnitude in the stronger regions of the prior art (i.e. at the bottom of the above-mentioned range of up to 50 μM), and preferably at a level of about the most active, more preferably of even stronger activity, than the compounds disclosed in the art. A further desire is to find compounds having oral antiviral activity.